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161.
A. O. Mustapha N. O. A. Oladipo S. B. Elegba 《Journal of Radioanalytical and Nuclear Chemistry》1994,181(2):343-350
The mean squared slowing-down distance, <r
2>, and the age to themal capture (Migration Area),M
2, are direct measures of the slowing-down, and the spreading out, processes of neutrons in a medium. They also enter directly into reactor calculations. These parameters have been determined experimentally for Am-Be neutrons (mean energy 4.46 Me V), in a block of perpex, using the activities induced in thin indium foils from the115In(n,)116In reactions. 相似文献
162.
Hossni Ziyat My Youssef Ait Itto Mustapha Ait Ali Abdellah Karim Abdelkhalek Riahi Jean‐Claude Daran 《Acta Crystallographica. Section C, Structural Chemistry》2002,58(2):o90-o93
The two new gem‐dihalogenocyclopropanes (1′S,3R)‐3‐(2′,2′‐dichloro‐1′‐methylcyclopropyl)‐6‐oxoheptanoic acid, C11H16Cl2O3, (2), and (1′S,3R)‐3‐(2′,2′‐dibromo‐1′‐methylcyclopropyl)‐6‐oxoheptanoic acid, C11H16Br2O3, (3), are isostructural. Both present two stereogenic centers at C1′ and C3. The absolute configuration was determined by X‐ray methods. The cyclopropyl rings are unsymmetrical, the shortest bond being distal with respect to the alkyl‐substituted C atom. 相似文献
163.
Mustapha Azreg-A?nou 《Monatshefte für Chemie / Chemical Monthly》2005,57(1):2017-2027
We investigated empirical data for the vapor pressure (154≤T≤196 K) and the heat capacity (12.52≤T≤189.78 K) of solid carbon dioxide. A computer algebra system (CAS) was used for all calculations. From the numerical point of view, we have adopted a cubic piecewise polynomial representation
for the heat capacity and reached an excellent agreement between the available empirical data and the calculated ones. Furthermore,
we have obtained values for the vapor pressure and heat of sublimation at temperatures below 195 right down to 0 K. The theoretical
key prerequisites are: 1) Determination of the heat of sublimation of 26250 J · mol−1 at vanishing temperature and 2) Elaboration of a ‘linearized’ vapor pressure equation that includes all the relevant properties
of the gaseous and solid phases. It is shown that: 1) The empirical vapor pressure equation derived by Giauque & Egan remains valid below the assumed lower limit of 154 K (a similar argument holds for Antoine’s equation), 2) The heat of sublimation reaches its maximum value of 27211 J · mol−1 at 58.829 K and 3) The vapor behaves as a (polyatomic) ideal gas even for temperatures below 150 K. 相似文献
164.
A structural study of amphiphilic PAMAM (poly(amido amine)) dendrimers in Langmuir and Langmuir-Blodgett films 总被引:2,自引:0,他引:2
Sui G Mabrouki M Ma Y Micic M Leblanc RM 《Journal of colloid and interface science》2002,250(2):364-370
Two amphiphilic PAMAM dendrimers are synthesized by attaching 12-hydroxydodecanoic acid (HA) chains to a poly(amido amine) (PAMAM) dendrimer core (including generation I and generation II). The limiting molecular area obtained from the surface pressure-area isotherm at the air/water interface suggests the edge-on configuration for both dendrimers in Langmuir films. The edge-on arrangement is also supported by the atomic force microscopic (AFM) studies of the Langmuir-Blodgett films. 相似文献
165.
Condensation of functionalized o-toluamide anions on a carbohydrate-derived lactone, followed by intramolecular aldol cyclization, provides enantiomerically pure 2-arylcyclohexenones. Different approaches for the stereoselective transformation of the carbonyl group of these key intermediates into an amino group were unsuccessful. However 1,4-addition of thiolate and concomitant ring closure to isocoumarine provided a useful method for the transformation of the tertiary amide function. Opening of the isocoumarin with ammonia provided the corresponding amide and recovery of the enone system. Subsequent reductive amination of this cyclohexenone was found to depend on the nature of the protecting groups and led to the protected form of 4-epi- and -iso-narciclasine. Oxo analogues of narciclasine and epi-narciclasine and lycoricidine were also obtained after reduction of the enone and subsequent lactonization. They showed no biological activity as antitumor agents. 相似文献
166.
Zaher M Baussanne I Ravelet C Halder S Haroun M Fize J Décout JL Peyrin E 《Journal of chromatography. A》2008,1185(2):291-295
In this paper, a new class of ligand-exchange chiral stationary phase (LE-CSP) based on the copper complexes of lipophilic aminoglycoside derivatives was reported. Different stationary phases were developed by coating reversed-phase liquid chromatography supports with three neamine derivatives carrying a lipophilic octadecyl chain at the 4', 5 and 6 positions, respectively. The enantioselective ability of these LE neamine-based CSPs was evaluated and the 4'-derivative coated column was found to be the most interesting one for the amino acid resolution. The effects of the variation of several chromatographic parameters on the enantioseparation were evaluated in order to identify the analysis optimal conditions. 相似文献
167.
Summary. We investigated empirical data for the vapor pressure (154≤T≤196 K) and the heat capacity (12.52≤T≤189.78 K) of solid carbon dioxide. A computer algebra system (CAS) was used for all calculations. From the numerical point of view, we have adopted a cubic piecewise polynomial representation
for the heat capacity and reached an excellent agreement between the available empirical data and the calculated ones. Furthermore,
we have obtained values for the vapor pressure and heat of sublimation at temperatures below 195 right down to 0 K. The theoretical
key prerequisites are: 1) Determination of the heat of sublimation of 26250 J · mol−1 at vanishing temperature and 2) Elaboration of a ‘linearized’ vapor pressure equation that includes all the relevant properties
of the gaseous and solid phases. It is shown that: 1) The empirical vapor pressure equation derived by Giauque & Egan remains valid below the assumed lower limit of 154 K (a similar argument holds for Antoine’s equation), 2) The heat of sublimation reaches its maximum value of 27211 J · mol−1 at 58.829 K and 3) The vapor behaves as a (polyatomic) ideal gas even for temperatures below 150 K. 相似文献
168.
Mustapha Lahyane 《Proceedings of the American Mathematical Society》2005,133(6):1593-1599
A -curve is a smooth rational curve of self-intersection , where is a positive integer. In 1998 Hirschowitz asked whether a smooth rational surface defined over the field of complex numbers, having an anti-canonical divisor not nef and of self-intersection zero, has -curves. In this paper we prove that for such a surface , the set of -curves on is finite but non-empty, and that may have no -curves. Related facts are also considered.
169.
Mustapha Lahyane 《Proceedings of the American Mathematical Society》2005,133(8):2219-2224
We give a characterization for a -divisor on a smooth rational surface to be irreducible under the assumption that an anticanonical divisor of is nef. Here is nef means for every effective divisor on , and a -divisor is a divisor such that the two numerical conditions hold.
As an application we give explicit examples of blowing up the projective plane at nine points infinitely near such that the obtained surface has an infinite number of -curves. A -curve is a smooth rational curve of self-intersection .
170.
Activated alkenes and dienes are converted into the corresponding alkenone in excellent yields (>90%). In aqueous acetonitrile, the transformations are catalyzed by 2,2,6,6-tetramethyl-1-oxopiperidinium (TEMPO+) in the presence of water and 2,6-lutidine. TEMPO+ cations were regenerated electrochemically from the radical parent (TEMPO) at a vitreous carbon anode. 相似文献